If I'm not wrong.. the OPTSTAT is the data stats related to the AWR, in which you have already cleaned. And so the statistics data can most probably be deleted with no harm.

try to find segments under WRI$_OPTSTAT* which consume more bytes:
SELECT segment_name,bytes
FROM dba_segments
WHERE segment_name in (
select table_name from dba_tables where tablespace_name = 'SYSAUX'
) order by bytes desc;